A common problem facing organizations today is the shortage of Internet Protocol (IP) version 4 (IPv4) addresses. Network Address Translation (NAT) is often used to alleviate the address shortage problem; however, numerous business-critical applications that require end-to-end communications do not function over NAT. Internet Protocol version 6 (IPv6) is an network layer protocol for packet-switched internetworks. IPv4 is currently the dominant Internet Protocol version, and was the first to receive widespread use. The Internet Engineering Task Force (IETF) has designated IPv6 as its successor for general use on the Internet. IPv6 has a much larger address space than IPv4, which allows flexibility in allocating addresses and routing traffic. The extended address length eliminates the need to use network address translation to avoid address exhaustion, and also simplifies aspects of address assignment and renumbering when changing Internet connectivity providers.
An organization's decision to adopt IPv6 raises a number of transition issues. For example, the first set of criteria to be evaluated for decision making, is the availability of existing network or application services in IPv6 networks, and whether new IPv6 services are accessible to users with only IPv4 connectivity. Until IPv6 completely replaces IPv4, a number of so-called transition mechanisms are needed to enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure. For example, Nordmark et al., RFC 4213, “Basic Transition Mechanisms for IPv6 Hosts and Routers,” Network Working Group, Internet Engineering Task Force (October 2005), describe dual stack and tunneling mechanisms to facilitate transition from IPv4 to IPv6. Dual stack refers to the use of network stacks that support both IPv4 and IPv6. An example of tunneling is the encapsulation of IPv6 packets with IPv4 headers to allow packets to be forwarded between IPv6 networks over IPv4 networks.